Introduction

The program_options library allows program developers to obtain
program options, that is (name, value) pairs from the user,
via conventional methods such as command line and config file.

Why would you use such a library, and why is it better than parsing
your command line by straightforward hand-written code?

It's easier. The syntax for declaring options is simple, and
the library itself is small. Things like conversion of option values to
desired type and storing into program variables are handled
automatically.

Error reporting is better. All the problems with the command line are
reported, while hand-written code can just misparse the input. In
addition, the usage message can be automatically generated, to
avoid falling out of sync with the real list of options.

Options can be read from anywhere. Sooner or later the command
line will be not enough for your users, and you'll want config files
or maybe even environment variables. These can be added without significant
effort on your part.